Method of application of dry lubricant to surface of an article

ABSTRACT

AN ARTICLE, SUCH AS A BEARING, HAVING A DRY LUBRICANT COATING IS MADE BY ELECTROPHORETICALLY DEPOSITING ON A BASE NEGATIVELY CHARGED PARTICLES, SUCH AS FLUOROCARBON POLYMERS, MOLYBDENUM DISULPHIDE, COPPER OXIDE OR RESINS, HAVING LUBRICATING PROPERTIES,SUBSTANTIALLY SIMULTANEOUSLY WITH THE ELECTROLYTIC DEPOSITION OF A METAL SUCH AS COPPER, GOLD, SILVER OR NICKEL. THIS CODEPOSITION IS ACCOMPLISHED BY PERIODICALLY REVERSING THE POLARITY OF THE OBJECT OR BASE TO BE COATED.

United States Patent 01 3,582,481 Patented June 1, 1971 hce 3,582,481 METHOD OF APPLICATION OF DRY LUBRICANT TO SURFACE OF AN ARTICLE Ralph J. Hovey, Glen Ellyn, and Afsar A. Khan, Chicago, Ill., assiguors to The Bunker-Ramo Corporation,

Broadview, Ill.

No Drawing. Continuation of application Ser. No. 520,359, Jan. 13, 1966. This application Apr. 3, 1970, Ser. No. 24,424

Int. Cl. C23b 5/50, 13/00; C23f 17/00 US. Cl. 204-42 Claims ABSTRACT OF THE DISCLOSURE An article, such as a bearing, having a dry lubricant coating is made by electrophoretically depositing on a base negatively charged particles, such as fluorocarbon polymers, molybdenum disulphide, copper oxide or resins, having lubricating properties, substantially simultaneously with the electrolytic deposition of a metal such as copper, gold, silver or nickel. This codeposition is accomplished 'by periodically reversing the polarity of the object or base to be coated.

The present application is a continuation of Ser. No. 520,359, filed Jan. 13, 1966, now abandoned.

This invention relates to dry lubricant, method of application thereof to the surface of an article, and a coated article so obtained.

Hitherto when dry lubricants, powders, waxes and liquid lubricants are applied to a surface, the particles and liquids, instead of adhering tenaciously to the surface, are, in most cases, largely removed after the first wipe.

An object of this invention is to provide a coating composition and a coating technique which allows control of how and where the lubricant is present and how much lubricant is on the surface at any moment.

Another object is to provide a coating composition and process of applying which gives a lubrication coating which supplies lubrication as the base material Wears.

Another object is to provide a coated article of superior lubrication properties.

Another object is to provide means for tailor making a bearing surface to meet specific requirements.

In accordance with this invention negatively charged particles having lubricating properties are electrophoretically deposited on a base substantially simultaneously with the electrolytic deposition of a metal such as copper, gold, silver, or nickel. This codeposition is accomplished by periodically reversing the polarity of the object or base to be coated whereby, assuming the object is first made the cathode, the metal will first be deposited, then on reversal of the polarity so that the object becomes an anode the negatively charged lubricating particles will be deposited, and so on through periodical reversals until a layer of the desired thickness is obtained.

The particles are deposited as a thin layer of discrete particles, for example, of .05 to .5 microns diameter (although 40 microns is operable), and the metal is deposited as a continuous thin layer over and partially around the particles so that the final result of multilayer deposition is a substantially homogeneous dispersion of particles in metal.

In order to prevent removal of one deposition before the other is made, the direct strike or deposition is made at a higher current density and for a longer time than the reverse strike. For example, the direct strike may be at a current density of 10 amperes per square foot While the reverse strike will be at 5-80 percent less current density. Likewise, the control time can be 230 seconds for the direct electrolytic deposition on the cathode with only 1-5 seconds for electrophoretic deposition when the polarity is reversed.

It should be understood that the current source may be a direct current source such as a battery or rectifier combined with suitable relays, reversing switches and resistances controlled by a timing mechanism to reverse the current at predetermined times and vary its value in accordance with the requirements of the article being coated, and the coating bath, care being taken as above mentioned to have the direct strike or deposition at a current density and time such as to prevent any substantial removal of one deposition before the other is made. The electric potential need not be above, and preferably is below the value at which electrolysis of water occurs. Suitable apparatus and electrical controls are Well known in the art, such as, for example, the electrical controls shown in Electroplating Engineering Handbook published by Reinhold Publishing Co., pp. 578-580 (1955).

The lubricating particles can be of any material having lubricating properties. Most of such materials in aqueous dispersions normally having or can be made to have a negative charge. Suitable materials include molybdenum disulphide, copper oxide, oxides, sulphides, and other compounds of metals and also plastics and resins known for their lubricating properties. Particularly satisfactory results, however, have been obtained with particles of fluorocarbon polymers. These include polytetrafluoroethylene, polychlorotrifiuoroethylene, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene hexafluoropropylene copolymer, vinylidene, fluoride-hexafluoropropylene copolymer, polyhexafluoropropylene, poly 1,1,1-trifluoropropylmethyl-dichlorosilane, fluorosilicone, elastomers, polyfluoroaniline, and copolymers of tetrafluoroethylene and trifluoronitrosomethane. The preferred fluorocarbons are those that are completely fluorinated, and of these the best, from the point of view of low coefficient of friction, is polytetrafluoroethylene. This material, under the trademark Teflon, is commercially available as negatively charged particles in an aqueous liquid.

The lubricating compositions can be applied to any surface such as, for example, ceramics and metals.

The treated surfaces can be used for bearings, including clock bearings; electrical contacts, hard-coat die surfaces, and dry lubrication of shells for military and space applications.

The treated parts exhibit low friction and extended wear.

The coatings give constant insertion and withdrawal forces to electrical contacts having low electrical resistance, and the contacts exhibit extended wearability.

The coatings may be of any thickness, but in general the composite layer is approximately .0001 inch total thickness for satisfactory results as a lubricant.

The following example gives a detailed procedure of carrying out the invention, it being understood that modifications of this procedure and the materials can be made and that the example is merely illustrative of a procedure which has been found satisfactory and is not intended to limit the invention thereto.

EXAMPLE I The base or substrate used was polished brass panels (4 inches by 2% inches) having a major surface area of 2 0 square inches. Steel panels were also used after 0.0002 inch thickness of initial copper plate.

The substrate Was made free of foreign materials, dirt, grease and oxides before processing. A water-break free surface is a good indication for adequate cleaning. The

following procedure for cleaning the brass panels was used:

(a) Degreased in perchloroethylene vapor for two minutes, followed by five minutes ultrasonic cleaning in perchloroethylene.

(b) Soaked clean for five minutes at room temperature in a solution of sodium carbonate (6 oz. per gal.), sodium cyanide (0.5 oz. per gal.) and preferably one percent of a wetting agent, followed by cold running water rinse.

(c) Electrocleaned in a solution of sodium carbonate (3 oz. per gal), trisodium phosphate (2 oz. per gal.), sodium cyanide (1 oz. per gal), and sodium hydroxide (0.5 oz. per gal.) 160 F. for 40 seconds direct strike and five seconds reverse polarity at 6 volts followed by two running water cold rinses for 30 seconds, while the rack holding the panel was moved briskly up and down and in swirling motion manually to rinse thoroughly.

(d) Neutralized dip in percent H 80 solution with manual swirling agitation of work for seconds followed by two running rinses, 30 seconds each.

(e) Striked in cyanide. copper solution of the following composition at 20 ASF125 F. for one minute, maintaining manual agitation of work.

Free NaCN 075-110 Followed by two rinses and a neutralized dip in 5 percent H 50 followed by another rinse. The work (copper panel) was then transferred to the plating tank.

The bath for electrophoretic and electrolytic deposition was prepared as follows:

24 ounces of CuSO .5H O, and 7.0 ounces of H SO (OR) was added to distilled or deionized water to make up two gallons of solution. This was treated with activated carbon at 5 g. per liter for 10 hours at room temperature, the solution filtered, and the filtrate transferred to a water jacketed glass tank of two gallons capacity, having means of heating and maintaining the temperature of the bath between 100-130 F. Teflon aqueous suspension No. 3170 (0.5% by weight negatively charged colloidal particles of polytetrafluoroethylene dispersed in Water acidulated with citric acid to a pH of 4 electrometric) was added directly to the electrolyte at 5 cc. per liter while stirring to insure uniform dispersion. The bath before and after the Teflon additive had a Baum of 10 B., a specific conductivity without the additive of 96,000 mhos./cm. and with the additive of 94,000 mhos./cm.

The brass panel was attached to a cathode rod agitator in the bath reciprocating at the rate of 28 strokes per minute.

A direct current of 10 to 40 amperes per square foot was applied for the first two minutes.

The anode on the direct strike consisted of copper slabs.

The power supply was then switched to a periodic reverse system with the following cycles:

Seconds Direct cycle 16 Reverse cycle 3 The current density of the reverse cycle was adjusted to 50 percent of the current density in the forward or direct cycle by means of a rheostat connected in series with the reverse cycle.

The process is feasible for rack as well as barrel plating.

The method can be carried out with other fluorocarbon polymers with little or no change in the conditions of the above example, and also with other lubricating particles by minor modifications apparent to those skilled in the art of electrolytic and electrophoretic deposition.

We claim:

1. In the method of making an article having a dry lubricant surface comprising electrolytically and electrophoretically depositing on a surface of the article a metal and particles. of a solid lubricant, the improvement wherein electrolytic and electrophoretic depositions on the surface of the article are carried out in a single bath containing positively charged metal ions and negatively charged lubricant particles by the passage of an electric current and periodically reversing the polarity while metal ions and lubricant particles are both present in the bath to deposit a metal matrix having solid lubricant particles dispersed therein.

2. The method of claim 1 wherein the current density for the electrophoretic deposition is 5 percent to percent less than the current density for the electrolytic deposition.

3. The method of claim 2 wherein the time of electrophoretic deposition is 1-5 seconds an dthe time of electrolytic deposition is 230 seconds.

4. A method according to claim 1 wherein the metal is selected from the group consisting of copper, gold, silver and nickel.

5. The method of making an article having a dry lubricant coating comprising solid lubricant particles dispersed in a metal matrix which comprises immersing the article in an electrolyte containing a solution of a metal salt supplying positive metal ions and negatively charged particles of a solid lubricant, making the article a cathode, passing an electric current through the electrolyte to electrolytically deposit metal on the cathode and periodically reversing the polarity after deposition of metal so as to make the article the anode and electrophoretically deposit the negatively charged particles on the article with the metal, the time of electrophoretic deposition being 1-5 seconds and the time of electrolytic deposition being 2-30 seconds.

6. The method of claim 5 wherein the particle of solid lubricant consists essentially of a fluorocarbon polymer.

7. The method of claim 6 wherein the fluorocarbon polymer is polytetrafluoroethylene.

8. A method according to claim 5 wherein the metal is selected from the group consisting of copper, gold, silver and nickel.

9. A method according to claim 5 wherein the metal salt is CuSO 10. The method of claim 5 wherein the particles of solid lubrciant are dispersed in substantially colloidal size in the electrolyte.

References Cited UNITED STATES PATENTS 2,858,256 10/1958 Fahnoe et a1. 204l6 2,999,798 9/1961 Eitel et al. 20438X 3,061,525 10/1962 Grazen 204-16X 3,197,389 7/ 1965 Dudek et al 204--40X 3,356,467 12/1967 Brown et al 204-38X 3,434,942 3/ 1969 Waterman 20438 3,461,044 8/1969 Lyons, Jr. et al. 204181X GERALD L. KAPLAN, Primary Examiner U.S. Cl. X.R.

2919l.2, 204-16, 38R, 38A, 38E, 46, 49, 52R, 181 

